1. Field of the Invention
This invention generally relates to hardware performance counters and, more specifically, to performance counters that provide two-dimensional monitoring capabilities.
2. Description of the Related Art
As the number and sophistication of processors, memories, buses, and other components increase, computer systems that may integrate many of these components have become more and more complex. For example, a popular architecture in commercial multiprocessing computer systems is the symmetric multiprocessor (SMP) architecture. Typically, an SMP computer system comprises multiple processors connected through a cache hierarchy to a shared bus. Additionally connected to the bus is a memory, which is also shared among the processors in the system. Processors are often configured with internal caches, and one or more caches are typically included in the cache hierarchy between the processors and the shared bus in an SMP computer system. Multiple copies of data residing at a particular main memory address may be stored in these caches. In order to maintain the shared memory model, in which a particular address stores exactly one data value at any given time, shared bus computer systems employ cache coherency. These systems, as well as other complex computer systems, typically employ complex protocols for purposes such as optimizing the system overall performance.
In the course of implementing these complex protocols, the way resources in the computer system are used and the way data contention occurs affect the overall system performance. A particular concern is the occurrence of xe2x80x9cbottleneckxe2x80x9d conditions. Bottleneck conditions may significantly alter the total time (i.e. the speed) that is needed to complete the execution of a set of instructions or a computation task. Further bottleneck conditions may occur in more than one component in the computer system. The occurrence and severity of bottleneck conditions depend on several factors such as the characteristics of the computer system, the task being performed, and the type of instructions being executed.
Performance counters have been used to identify bottleneck conditions in computer systems. They may be used to evaluate a system""s performance and subsequently to optimize its performance. Performance counters can be implemented either hardware or software. Both hardware and/or software performance counters have been used in evaluating and optimizing the performance of computer systems.
Software performance counters typically monitor a particular component through the execution of a set of instructions. Since the software performance counter has itself to be executed by the computer system, an operating aspect of the component being monitored may be needed to execute the software. Therefore software performance counters have a potential to interfere with the operation of the component being monitored. Such interference may affect the accuracy of the evaluation results that are sought by employing the software performance counter.
Hardware performance counters may be employed to monitor specific signals associated with the operation of a component. Hardware performance counters may be designed as embedded units within the components to be monitored or within the computer system. Typically, no execution of software is needed to operate the hardware performance counter. Accordingly, they tend to interfere less with the operation of the components being monitored when compared to software performance counters.
To monitor the performance of a component within a computer system, the hardware performance counter may be set to monitor the occurrence of a specific event within the component for a specific period of time, or monitoring period. Unfortunately, in many situations, the monitoring data obtained by such performance counters typically does not provide enough information to precisely and thoroughly evaluate bottleneck and/or other operating conditions. Therefore, the designer may have insufficient information to modify the system for optimal performance, or may otherwise consume much time and effort to optimize the system design. Accordingly, a hardware performance counter is desired to provide a more comprehensive evaluation of a computer system component.
The problems outlined above are in large part solved by a performance counter to monitor a plurality of events that may occur in a component within a computer system during a monitoring period or testing period. The monitoring results, which are provided upon completion of the performance testing, may be used to provide histogram representations of the component performance. In one embodiment, the performance counter comprises a first storage, a second storage, programmable control logic, and a counting mechanism. The first storage is configured to store information indicative of a plurality of events to be monitored and the monitoring period for each event. The second storage is configured to store counting results obtained during the testing period. A counting mechanism, which is coupled to the second storage, is configured to monitor the occurrence of the events in the component under test. The counting mechanism is coupled to the control logic and the control logic is coupled to the first storage.
The control logic is configured to control the counting mechanism based upon the information stored in the first storage such that two or more events are counted during the monitoring period. The counting results include a count for each event from the events being monitored during the monitoring period. Thus, the count is indicative of a frequency of occurrence of the corresponding event. Advantageously, the performance counter provides two-dimensional data on the performance of the component under test. Accordingly, the monitoring data may be used to develop a histogram performance representation that provides the designer with accurate and precise evaluations of the system performance.
The performance counter may be embedded within a system memory, a cache, a cache controller, a bus, a buffer, an interconnect, a queue, a snoop controller, a processor, an input/output device, or other component within the computer system. Further, two or more performance counters may be employed to monitor two or more components within the computer system during the same monitoring or testing period.